Stabilizing center drive link for saw chain

ABSTRACT

A chain comprised of a conventional sequence of pivotally connected links some of which links have extensions for engaging objects, e.g., links wherein the extensions have sharpened edges for engaging and cutting trees. The novelty being the provision of links preceding and following the links having the extensions provided with forwardly projected portions and rearwardly projected portions. The rearwardly projected portions underlie the forwardly projected portions of the following links to restrict independent pivotal movement via leverage action.

United States Patent [1 1 Ross, Jr.

STABILIZING CENTER DRIVE LINK FOR SAW CHAIN [75] Inventor: Cecil John Ross, Jr., Portland, Oreg.

[73] Assignee: Omark Industries, Inc., Portland,

Oreg.

[22] Filed: June 1, 1972 [21] Appl. No.: 258,651

[52] US. Cl. 83/833, 83/830 [51] Int. Cl B27b 33/14 [58] Field of Search 83/830, 831, 832, 83/833, 834

[56] References Cited UNITED STATES PATENTS 3,176,733 4/1965 Dobbertin 83/834 3,542,096 11/1970 Oehrli 83/830 [451 July 31,1973

3,608,595 9/1971 Oehrli 83/830 Primary ExaminerDonald R. Schran Att0rneyRobert L. Harrington [57] ABSTRACT A chain comprised of a conventional sequence of pivotally connected links some of which links have extensions for engaging objects, e.g., links wherein the extensions have sharpened edges for engaging and cutting trees. The novelty being the provision of links preceding and following the links having the extensions provided with forwardly projected portions and rearwardly projected portions. The rearwardly projected portions underlie the forwardly projected portions of the following links to restrict independent pivotal movement via leverage action.

4 Claims, 3 Drawing Figures 24 its 124 STABILIZING CENTER DRIVE LINK FOR SAW CHAIN HISTORY This invention relates to stabilizing links in a sequence of chain links to restrict independent pivotal movement of certain links in the sequence. In particular, the stabilizing links are applicable for restricting a cutting link of a saw chain from rearing back as is typical during the cutting operation of conventional saw chain. It will be understood, however, that similar restriction of pivotal movement is desireable in comparable chain uses, e.g., conveyor chain.

Conventional saw chain available on the market is provided with a repeating sequence of pivotally connected center drive links and side links. Certain of the side links include projections having cutting edges. (Such side links are hereafter referred to as cutting links.) It will be understood that as the cutting links are cutting, e.g., for felling a tree, the acting forces are applied in a manner to urge rearward pivoting of the cutting links. This rearward pivotal force is erratic and produces a buffering effect that detrimentally affects cutting efficiency, ease of handling, and wearing of the chain, sprocket and guide bar. A number of patents have been issued for inventions which purport to obviate this problem. Notable of such patents are Dobbertin, US. Pat. No. 3,176,733; Silvon, U.S. Pat. No. 3,283,789; and Oehrli, US. Pat. No. 3,542,096. It is believed that the Dobbertin patent is the most pertinent in that it also recognizes the advantage of providing mechanical connection between successive drive links.

However, the manner in which Dobbertin provides this mechanical connection is significantly different that the present invention.

In brief, the present invention includes an interconnection between adjacent center links whereby a forwardly projected portion of one center link overlaps a rearwardly projected portion of the preceding center link. This interconnection is designed so that the center links can be pivoted together but because of the overlapping interconnection, the rear end of the front center link cannot be raised without also raising the front end of the following center link. Whereas the front and rear pivotal connections of the cutting links are connected to successive center drive links, the front of the cutting link cannot be raised (rearing back) without either raising both center links or causing rearward pivoting of the front center link. Chain tension resists such rearward pivoting of the center link and this reduces the undesireable rearing back of the cutting link.

The invention will be further clarified by referece to the following detailed description and drawings wherein:

FIG. 1 illustrates a saw chain of the present invention as mounted on the straight reach of a chain saw guide bar;

FIG. 2 illustrates the saw chain of FIG. 11 passing around a sprocket; and

FIG. 3 is a perspective view illustrating the interconnecting arrangement of adjacent center drive links.

Referring to the drawings, FIG. 1 illustrates a section of saw chain including center drive links 10, side links 12 and cutting links 14. Side links have been removed from selected positions in the sequence for purposes of illustration. It will be understood that for every cutting link and side link shown, on the opposite side of the center links, there are corresponding side links. The links are pivotally interconnected by rivets 16. Each of the cutting links 14 include a body portion 18 similar in structure to the side links 12 but including extensions forming a cutter 20 and depth gauge 22. The center links 10 include downwardly projected portions 24 (as viewed in FIG. I). These downwardly projected portions are adapted to ride in a groove 26 formed in a guide bar 28 of a chain saw (only a portion of which is illustrated in FIG. 1). It will further be understood that the cutting links 14 and side links 12 are adapted to ride on upper edge 30 provided on each side of the groove of the guide bar. The downwardly projected portions 24 provide the means for a sprocket 32 (shown in FIG. 2) to engage these downwardly projected portions to drive the saw chain around the bar of the chain saw.

The present saw chain is differentiated from conventional saw chain in the provision of the forwardly projected portions 34 and rearwardly projected portions 36 of the center drivelinks 10. As viewed in FIG. 3, it will be seen that the forwardly projected portion 34 is generally above a center line 40 (drawn through the rivet holes 38) with a bottom edge forming an upper shoulder 34a. The rearwardly projected portion 36 is generally below the center line 40 with an upper edge forming a lower shoulder 36a adapted to abut the shoulder 34a when the adjacent links are aligned as shown in FIG. 1 and FIG. 3. It will be understood that although the rearward and forward extensions can be any of a number of configurations, it is considered to be an advantage for the rearward extension to be shorter than the forward extension to avoid binding as the chain bends around the sprocket.

Although the center drive links 10 are each provided with forward and rearward projections 34 and 36, the interconnection is desired primarily at the positions where the interconnection is bridged by a cutting link 14. Hereafter, reference to front and back center links is intended as being relative to the interconnection bridged by a cutting link. The cutting force acting against the cutting edge 41 urges pivoting of the cutting link with a force acting to push down on the rear end of the cutting link and acting to raise the front end. As the front end of the cutting link is raised, the front rivet is raised, which rivet is also the rear rivet of the front center link. The front of the back center link is held down by reason of its rivet connection with the rear end of the cutting link. It follows that the forwardly projected portion 34 holds down or anchors the rearwardly projected portion 36 of the front center link and in order for the front end of the cutting link to be raised, it must raise the front end of the front center link pivotally about the anchor point established by the overlapping engagement. Because of the short distance between the anchor point and the rivet connection, the front end of the forward center link is raised to a much greater degree than the cutting link, creating an imbalance of effective leverage forces so that the normal chain tension acting to hold the front end of the center link in alignment, effectively resists the objectionable rearing back of the cutting link.

It will be understood, particularly with reference to FIG. 2, that there is no interference preventing the front and back center links from being pivoted together and in opposite directions, that is with the overlapping projected portions both being raised or both being lowered. It is to be noted, however, that there is some stabilizing effect retained during travel of the chain around the curved path of the sprocket as illustrated in the first two positions of the center links. At some point just prior to being returned to the straight part of the bar, there is a separation as shown. Because some binding may occur just as the front center link enters the curvature, it may be desireable for the forward projection to be made longer than the rearward projection.

The center links of the present chain design have interengaging shoulder portions with contacting surfaces defining an anchor point (which point I may move slightly during pivoting) located rearward of the forward rivet connection (rear rivet connection of the front center link and front rivet connection of the cutting link). It. is not considered necessary for the anchor point to be aligned with the rivet connections. However, it is considered necessary for the anchor point to be positioned within the arc defined by the pivoting of said forward rivet connection about the rear end of the cutting link. Note that if the pivotingof the said forward rivet connection creates an effective line of force forward the anchor point established by the contacting overlapping surfaces, the front center link is prevented from pivoting and the chain becomes stiff, creating hazards of kick back and making it difficult to handle. The above also distinguishes the present chain over that of the Dobbertin patent reference previously noted.

Those skilled in the art will be aware of numerous modifications without departing from the scope of the invention. Accordingly, the patent is not intended to be limited to the above described embodiment, but it is intended to be encompassed by the appended claims.

What is claimed is:

1. A chain of interconnected links adapted to be driven on a predetermined guide track whereby the chain is placed in tension comprising: a sequence of chain links, one of said links in said sequence having an outer extension for engaging an object whereby rearward pivoting thereof is urged, said engaging link having a front pivotal connection with a preceding link and a rear pivotal connection with a following link, both of said preceding and following links being on the same side of the engaging link, said preceding link having a portion projected rearwardly of said front pivotal connection and said following link having a portion projected forwardly of said rear pivotal connection, said forwardly projected portion of said following link overlapping said rearwardly projected portion of said preceding link, said rearwardly and forwardly overlapping projected portions being in contact upon upward movement of the preceding link relative to the following link, said contacting overlapping portions providing an anchor point rearward of the arc generated by pivoting of said front pivotal connection as induced by pivoting of said engaging link, said anchor point being a pivot about which the preceding link pivots outwardly as urged by pivoting of said engaging link and as resisted by the chain tension.

2. A saw chain adapted to be drivingly entrained on the saw chain guide bar of a chain saw comprising: a sequence of saw chain links, one of said links in said sequence having an outer extension with a sharpened forward edge providing a cutting link in said sequence, said cutting link having a frontpivotal connection with a preceding link and a rear pivotal connection with a following link, both of said preceding and following links being on the same side of the cutting link, said preceding link having a portion projected rearwardly of said front pivotal connection and said following link having a portion projected forwardly of said rear pivotal connection, said forwardly projected portion of said following link overlapping said rearwardly projected portion of said preceding link, said rearwardly and forwardly overlapping projected portions being in contact upon upward movement of the preceding link relative to the following link, said contacting overlapping portions providing an anchor point rearward of the are generated by pivoting of said front pivotal connection as induced by pivoting of said engaging link, said anchor point being a pivot about which the preceding link pivots upon continuing upward movement of the preceding link as induced by upward pivoting of the front pivotal connection.

3. A saw chain as defined in claim 2 wherein the forwardly projected portion includes a lower shoulder and the rearwardly projected portion includes an upper shoulder, said lower shoulder superimposed on said upper shoulder when the saw chain is entrained on a straight reach, and said super-imposed shoulder portions being in general alignment with a center line drawn through the pivotal connections.

4. A saw chain as defined in claim 3 wherein the rearwardly projected portion of the front center link is shorter than the forwardly projected portion of the rear link to reduce binding as the saw chain 'is curved around the end of the guide bar. 

1. A chain of interconnected links adapted to be driven on a predetermined guide track whereby the chain is placed in tension comprising: a sequence of chain links, one of said links in said sequence having an outer extension for engaging an object whereby rearward pivoting thereof is urged, said engaging link having a front pivotal connection with a preceding link and a rear pivotal connection with a following link, both of said preceding and following links being on the same side of the engaging link, said preceding link having a portion projected rearwardly of said front pivotal connection and said following link having a portion projected forwardly of said rear pivotal connection, said forwardly projected portion of said following link overlapping said rearwardly projected portion of said preceding link, said rearwardly and forwardly overlapping projected portions being in contact upon upward movement of the preceding link relative to the following link, said contacting overlapping portions providing an anchor point rearward of the arc generated by pivoting of said front pivotal connection as induced by pivoting of said engaging link, said anchor point being a pivot about which the preceding link pivots outwardly as urged by pivoting of said engaging link and as resisted by the chain tension.
 2. A saw chain adapted to be drivingly entrained on the saw chain guide bar of a chain saw comprising: a sequence of saw chain links, one of said links in said sequence having an outer extension with a sharpened forward edge providing a cutting link in said sequence, said cutting link having a front pivotal connection with a preceding link and a rear pivotal connection with a following link, both of said preceding and following links being on the same side of the cutting link, said preceding link having a portion projected rearwardly of said front pivotal connection and said following link having a portion projected forwardly of said rear pivotal connection, said forwardly projected portion of said following link overlapping said rearwardly projected portion of said preceding link, said rearwardly and forwardly overlapping projected portions being in contact upon upward movement of the preceding link relative to the follOwing link, said contacting overlapping portions providing an anchor point rearward of the arc generated by pivoting of said front pivotal connection as induced by pivoting of said engaging link, said anchor point being a pivot about which the preceding link pivots upon continuing upward movement of the preceding link as induced by upward pivoting of the front pivotal connection.
 3. A saw chain as defined in claim 2 wherein the forwardly projected portion includes a lower shoulder and the rearwardly projected portion includes an upper shoulder, said lower shoulder superimposed on said upper shoulder when the saw chain is entrained on a straight reach, and said super-imposed shoulder portions being in general alignment with a center line drawn through the pivotal connections.
 4. A saw chain as defined in claim 3 wherein the rearwardly projected portion of the front center link is shorter than the forwardly projected portion of the rear link to reduce binding as the saw chain is curved around the end of the guide bar. 